Pigmentation in the skin such as pigmented spots and freckles are resulted from hyperpigmentation of melanin in the epidermis. The hyperpigmentation is caused by acceleration of melanin production in epidermal melanocytes triggered by hormone abnormality or UV stimulation.
A whitening agent has been mixed into a skin external preparation with an aim to prevent and improve such abnormal melanin pigmentation. At present, as ingredients that are mixed into a skin external preparation as a whitening agent, there are vitamin C derivative, kojic acid, arbutin (4-hydroxyphenyl-β-D-glucopyranoside), Rucinol (4-n-butylresorcinol), ellagic acid, etc, which are known to have an inhibitory action on melanin production.
However, a whitening agent fully satisfactory in terms of the effect, safety, and the like has not yet been obtained, and therefore development of a new whitening agent has been demanded.
On the other hand, Patent Literature 1 describes a pyrazole pyrimidine compound having a regulatory action on a potassium channel.
Also, Patent Literatures 2 to 4 describe a pyrazole pyrimidine compound having a pest control activity on rice blast disease, leaf blight disease of rice and sesame, cucumber powdery mildew, and the like.
Further, Patent Literature 5 describes a pyrazole-pyrimidine compound useful as an analgesic.
However, these literatures are totally silent on an inhibitory action on melanin production and a whitening effect.    Patent Literature 1: WO2006/100212    Patent Literature 2: Japanese Unexamined Patent Publication No. S54-117029    Patent Literature 3: Japanese Unexamined Patent Publication No. S54-147921    Patent Literature 4: Japanese Unexamined Patent Publication No. S62-404    Patent Literature 5: Japanese Examined Patent Publication No. S42-19593